Signal generator with frequency offset unit in the base band

ABSTRACT

A signal generator comprises at least one first base band unit and a second base band unit, generating a digital base band signal. At least one first frequency offset unit, connected to the first base band unit, which adds the output signal form the second base band unit and the output signal from the frequency offset unit and an I/Q modulator, in series with the addition unit are provided.

FIELD OF THE INVENTION

[0001] The invention relates to a signal generator, in which a digitalbase band signal is first generated by means of a base band unit, andsubsequently—optionally after the insertion of units capable ofsimulating a transmission channel e.g. with fading, distortion andnoise—supplied to a I/Q modulator.

BACKGROUND OF THE INVENTION

[0002] In mobile telephone technology, a broad-band amplifier, which canbe used to amplify several mobile telephone signals at the same time, isincreasingly used in order to economise on costs. For instance, two ormore W-CDMA (Wideband—Code Division Multiple Access) signals positionedon different frequency bands, or a GSM signal and a W-CDMA signal may berequired at the same time. In order to test a power amplifier in a basestation, for example, this power amplifier must be supplied with ameasurement signal, which simulates the operational situation as closeto reality as possible, i.e. with a combined signal derived from the twoabove-named individual signals. For this purpose, the individual signalshave, hitherto, been generated in separate signal generators as separatehigh-frequency signals, which are then combined at the output of thesignal generators, i.e. at the high-frequency side. This raises theproblem of synchronising the two separate signal generators. Moreover,it is disadvantageous that several signal generators are needed, becauseit is difficult to operate several separate devices, and the devicesrequire complex wiring at the output side.

[0003] Regarding background art, reference is made, by way of example,to U.S. Pat. No. 5,465,050, wherein the output signal from a signalgenerator is combined on the high-frequency side, via a resistornetwork, with the output signal from a noise generator.

SUMMARY OF THE INVENTION

[0004] The invention addresses therefore a need for creating a signalgenerator, capable of generating digitally-modulated signals modulateduniformly or differently and positioned in different frequency bands ina simple manner.

[0005] According to an embodiment of the invention, at least two baseband units are provided, wherein the output signals from the base bandunits are already offset relative to one another in the base band, andwherein the base band signals offset with regard to their frequencyposition are added. For example, two W-CDMA signals can be generated,which are offset in their frequency position by a few MHz relative toone another.

[0006] The advantage of this procedure is that the combined signal canbe generated with a single signal generator, and several signalgenerators need not be interconnected at the high frequency side. Thisensures ease of handling.

[0007] The base band units can be controlled in a synchronous manner bya common control unit, i.e. by a common microprocessor, a common digitalsignal processor or a common synthesiser. There is therefore nosynchronisation problem as encountered when using two separate signalgenerators. Optionally, approximately the same setting may be adoptedfor both base band units, and the user need only adjust the appropriateparameter once on the device for both base band units.

[0008] A base band generator, to which external signals can be supplied(analogue or digital, e.g. I/Q-data or an intermediate frequency signal)can be provided. The digital base band signal, which is generated fromthis externally supplied signal, can also be offset in frequency.

[0009] Furthermore, units which simulate certain channel properties,e.g. fading units, noise units or distortion units can be insertedbetween the base band units and the I/Q-modulators. In this context, asan alternative, the base band signals need not be added to the combinedsignal until after the fading units and/or the noise units.

[0010] Still other aspects, features, and advantages of the presentinvention are readily apparent from the following detailed description,simply by illustrating a number of particular embodiments andimplementations, including the best mode contemplated for carrying outthe present invention. The present invention is also capable of otherand different embodiments, and its several details can be modified invarious obvious respects, all without departing from the spirit andscope of the present invention. Accordingly, the drawing and descriptionare to be regarded as illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] An exemplary embodiment of the invention is described in greaterdetail below with reference to the drawing. The drawing is as follows:

[0012]FIG. 1 shows a block circuit diagrams of an exemplary embodimentof a signal generator according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013] The signal generator 1 provides a first base band unit 2 a and asecond base and unit 2 b. The base band units 2 a and 2 b generate attheir I and Q outputs base band signals according to predeterminedstandards, which can be selected by the user, for example, according tothe GSM standard, the GSM-EDGE standard or the Wideband-CDMA standard.The base band signals 2 a, 2 b can be supplied with clock signals atbushes 3 a and/or 3 b; trigger signals at bushes 4 a and/or 4 b; andmodulation data at bushes 5 a and/or 5 b. Alongside these, in theexemplary embodiment illustrated, a digital base band generator 6 isprovided, which generates the I- and Q-components of a further base bandsignal from digital I/Q-values supplied to a bush 7. The output signalfrom the digital base band generator 6 can be frequency-offset via amultiplication unit 8 c, to which the adjustable frequency of anadjustable local oscillator 9 c is supplied. The multiplication unit 8 cand the local oscillator 9 c therefore form a frequency-offset unit 40c.

[0014] The optionally frequency-offset base band signal from the digitalbase band generator unit 6 is supplied via a first switch element 10 aand/or a second switch element 10 b to a digital addition unit lla or adigital addition unit 11 b.

[0015] The output signal from the base band unit 2 a is supplied to amultiplication unit 8 a consisting in each case of a multiplier for theI-component and for the Q-component. The adjustable frequency of anadjustable local oscillator 9 a is supplied to the multiplication unit 8a. Accordingly, the digital output signal from the base band unit 2 acan be frequency-offset if required. If no frequency offset is required,the multiplier of the multiplication unit 8 a can be bypassed by meansof switchable rerouting lines. The output signal from the multiplicationunit 8 a is supplied to the addition unit 11 a.

[0016] In a similar manner, the output signal from the base band unit 8b is supplied to a multiplication unit 8 b, consisting in each case of amultiplier for the I-component and the Q-component. The multipliers ofthe multiplication unit 8 b are connected to the adjustable localoscillator 9 b, so that the frequency of the digital output signal fromthe base band unit 2 b can be frequency offset if required. If nofrequency offset is required, the multipliers of this multiplicationunit 8 b can also be bypassed by means of switchable rerouting lines.The output signal from the multiplication unit 8 b is supplied to theaddition unit 11 b.

[0017] The output from the multiplication unit 40 a can also beconnected via a switch element 41 a to the addition unit 11 b, while theoutput from the multiplication unit 8 b can be connected via a switchelement 41 b to the addition unit 11 a.

[0018] In this manner, the output signals from the base band unit 2 a,the base band unit 2 b and the base band generator 6 can be frequencyoffset independently from one another and added with a frequency-offseteither to the addition unit lla or the addition unit 11 b.

[0019] The output signal from the addition units 11 a and 11 b can besupplied via a switch element 12 a and/or a switch element 12 b to afading unit 13 a and/or 13 b, which applies fading (variable decrease)and/or distortion to the base band signal. The functions of the fadingunits 13 a and 13 b, such as the number, the time delay and the dampingof the signal-delay pathways implemented in the fading unit, can bedetermined by the user. The fading units 13 a and 13 b are eachconnected via an addition unit 14 a and/or 14 b to a noise unit 15 aand/or 15 b. The noise units 15 a, 15 b apply a noise signal, which canbe determined by the user, to the base band signal. For example, thetype of noise and the level of the noise signal generated by the noiseunit 15 a, 15 b can be selected by the user.

[0020] The output signals from the fading units 13 a, 13 b can also beadded and in each case supplied to one of the two noise units 15 aand/or 15 b via a switch element 16 connecting the addition units 14 aand 14 b instead of connecting the relevant fading unit 13 a and/or 13 bseparately to the allocated noise unit 15 a and/or 15 b. The I/Q outputsignals at the output of the noise units 15 a and/or 15 b can beextracted at bushes 17 a and 18 a and/or 17 b and 18 b.

[0021] The output signals from the noise units 17 a and 17 b can besupplied to I/Q-modulators 20 a and/or 20 b via addition and switchunits 19 a and 19 b. In this case also, the output signals from thenoise units 15 a and 15 b can be added via a switch element 21 andsupplied to one of the two I/Q-modulators 20 a and/or 20 b. Severaluser-specific selection options are also available with regard to thefunction of the I/Q modulator 20 a, 20 b. For example, the I/Q-modulator20 a, 20 b can be operated to generate a burst sequence, and the activebursts and/or the level of the active bursts can be selected by theuser.

[0022] In each case, the I/Q-modulators 20 a and 20 b are connected to ahigh-frequency unit 22 a and/or 22 b, and a high-frequency signal can bepicked up at a bush 23 a and/or 23 b. For example, the output frequency,or several output frequencies initiated according to thesudden-frequency-change process from the high frequency unit 22 a and 22b, can be selected by the user.

[0023] Additionally, a signal display 24 is available, which can beconnected via switch elements 25 a and/or 25 b in the exemplaryembodiment to the output of the noise unit 15 a or the noise unit 15 b.Alternatively, it is also conceivable for the display device 24 to beconnected directly to the outputs from the base band units 2 a and 2 b.For instance, the signal display 24 allows the configuration diagram tobe displayed, so that the user can check the method of operation of theconnected signal pathway.

[0024] A Bit Error Rate Tester (BERT) 26 is also provided, and a signalfrom the device under test (DUT) can be supplied to the input bush 27 ofthe BERT 26, so that the bit error rate of the signal can be deducted atthe output bush 28.

[0025] Other functional units may also be present and variantcombinations of the functional units may be possible. These have notbeen explained here for the sake of simplicity.

[0026] Using a combination unit 42, such as a directional coupler or aresistor network, the outputs 23 a and 23 b from the high-frequencyunits 22 a and 22 b may optionally be capable of further combinationallowing the two signal pathways to be added on the high frequency side,if required, to form a combined signal. Accordingly, the twofrequency-offset base band signals may optionally each be modulated ontwo separate high-frequency pathways, so that only the two analoguehigh-frequency signals are added. If the addition is carried out in thebase band, the attainable signal dynamics are limited by theanalogue-digital converter. This disadvantage is not encountered if theaddition is implemented in the analogue range. However, a greater degreeof complexity is required in this case. In this context, the two highfrequency pathways operate with the same carrier frequency. By contrastwith the solution of operating both high-frequency pathways withdifferent carrier frequencies and dispensing with the frequency offsetin the base band, this provides the advantage that only one frequencygenerator unit, for example, only one synthesiser, is needed to generatethe carrier frequency. This clearly leads to a reduction in complexity.

[0027] All of the functional units described above: 2 a, 2 b, 6, 8 a, 8b, 8 c, 9 a, 9 b, 9 c, 10 a, 10 b, 11 a, 11 b, 12 a, 12 b, 13 a, 13 b,14 a, 14 b, 15 a, 15 b, 16, 19 a, 19 b, 20 a, 20 b, 21, 22 a, 22 b, 24,26, 40 a, 40 b, 41 a, 41 b, 42 are connected to a control unit 28, forexample, a CPU, via a control bus 29. Connections to the functionalunits are indicated by the symbol (*). The control unit 28 controls theconfiguration and function of the individual functional units requiredby the user. The current configuration of the functional units can bedisplayed on a display device 29, which can be disposed, together withthe operating elements 30, at the front of the signal generator 1. Forthis purpose, a graphic functional block is allocated to each functionalunit, and the connection of the functional units is displayed on thedisplay device 29 through corresponding connecting elements, whichconnect the functional blocks to one another. The connections betweenfunctional blocks and the function of the functional blocks are selectedeither by means of a rotary knob 31, appropriate operating buttons 32and/or via a mobile positioning element 33 (mouse).

[0028] While the present invention has been described in connection witha number of embodiments and implementations, the present invention isnot so limited but covers various obvious modifications and equivalentarrangements, which fall within the purview of the appended claims.

1. A signal generator comprising: at least one first base band unit anda second base band unit, configured for a digital base band signal, atleast one first frequency offset unit, coupled to the first base bandunit and configured for offsetting a frequency of an output signal fromthe first base band unit by a frequency offset, at least one firstaddition unit, configured for adding an output signal from the secondbase band unit and an output signal from the first frequency offsetunit, and an I/Q-modulator coupled in series to the first addition unit.2. A signal generator according to claim 1, further comprising: a secondfrequency offset unit, coupled to the second base band unit (2 a) andconfigured for offsetting a frequency of the output signal from thesecond base band unit by a frequency offset, a second addition unitconfigured for adding the output signal from the first base band unitand the output signal from the second frequency offset unit, and asecond I/Q-modulator coupled in series to the second addition unit.
 3. Asignal generator according to claim 1, wherein the base band units arecontrolled in a synchronous manner by a common control unit.
 4. A signalgenerator according to claim 1, further comprising: a base bandgenerator, to which an external signal can be supplied, configured forgenerating a digital base band signal from the external signal, and afurther frequency offset unit, coupled to the base band generator andconfigured for offsetting the frequency of the output signal from thebase band generator by a frequency offset, wherein the output signalfrom the further frequency offset unit can be supplied to the firstand/or second addition unit.
 5. A signal generator according to claim 2,further comprising separate high frequency units connected in series toeach of the I/Q-modulators wherein the output signals from the highfrequency units can be combined in a combination unit.
 6. A signalgenerator according to claim 1, further comprising: a fading unitconfigured for applying fading and/or distortion to the base bandsignal, and connected in series to each base band unit, and at least onefurther addition unit coupled in series to the fading units, by means ofwhich output signals from the fading units can be added.
 7. A signalgenerator according to claim 1, further comprising: a noise unitconfigured for applying noise to the base band signal, and connected inseries to each base band unit, and at least one further addition unitcoupled in series to the noise units, by means of which output signalsfrom the noise units can be added.